From d3a84a8d0dde4e26bc084b36ffcbdc5932ac85e2 Mon Sep 17 00:00:00 2001
From: Max Staudt <max@enpas.org>
Date: Thu, 27 Aug 2020 17:49:00 +0200
Subject: [PATCH] affs: fix basic permission bits to actually work
Git-commit: d3a84a8d0dde4e26bc084b36ffcbdc5932ac85e2
Patch-mainline: v5.9-rc4
References: git-fixes

The basic permission bits (protection bits in AmigaOS) have been broken
in Linux' AFFS - it would only set bits, but never delete them.
Also, contrary to the documentation, the Archived bit was not handled.

Let's fix this for good, and set the bits such that Linux and classic
AmigaOS can coexist in the most peaceful manner.

Also, update the documentation to represent the current state of things.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Max Staudt <max@enpas.org>
Signed-off-by: David Sterba <dsterba@suse.com>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>

---
 fs/affs/amigaffs.c |   27 +++++++++++++++++++++++++++
 fs/affs/file.c     |   26 +++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 1 deletion(-)

--- a/fs/affs/amigaffs.c
+++ b/fs/affs/amigaffs.c
@@ -419,24 +419,51 @@ affs_mode_to_prot(struct inode *inode)
 	u32 prot = AFFS_I(inode)->i_protect;
 	umode_t mode = inode->i_mode;
 
+	/*
+	 * First, clear all RWED bits for owner, group, other.
+	 * Then, recalculate them afresh.
+	 *
+	 * We'll always clear the delete-inhibit bit for the owner, as that is
+	 * the classic single-user mode AmigaOS protection bit and we need to
+	 * stay compatible with all scenarios.
+	 *
+	 * Since multi-user AmigaOS is an extension, we'll only set the
+	 * delete-allow bit if any of the other bits in the same user class
+	 * (group/other) are used.
+	 */
+	prot &= ~(FIBF_NOEXECUTE | FIBF_NOREAD
+		  | FIBF_NOWRITE | FIBF_NODELETE
+		  | FIBF_GRP_EXECUTE | FIBF_GRP_READ
+		  | FIBF_GRP_WRITE   | FIBF_GRP_DELETE
+		  | FIBF_OTR_EXECUTE | FIBF_OTR_READ
+		  | FIBF_OTR_WRITE   | FIBF_OTR_DELETE);
+
+	/* Classic single-user AmigaOS flags. These are inverted. */
 	if (!(mode & 0100))
 		prot |= FIBF_NOEXECUTE;
 	if (!(mode & 0400))
 		prot |= FIBF_NOREAD;
 	if (!(mode & 0200))
 		prot |= FIBF_NOWRITE;
+
+	/* Multi-user extended flags. Not inverted. */
 	if (mode & 0010)
 		prot |= FIBF_GRP_EXECUTE;
 	if (mode & 0040)
 		prot |= FIBF_GRP_READ;
 	if (mode & 0020)
 		prot |= FIBF_GRP_WRITE;
+	if (mode & 0070)
+		prot |= FIBF_GRP_DELETE;
+
 	if (mode & 0001)
 		prot |= FIBF_OTR_EXECUTE;
 	if (mode & 0004)
 		prot |= FIBF_OTR_READ;
 	if (mode & 0002)
 		prot |= FIBF_OTR_WRITE;
+	if (mode & 0007)
+		prot |= FIBF_OTR_DELETE;
 
 	AFFS_I(inode)->i_protect = prot;
 }
--- a/fs/affs/file.c
+++ b/fs/affs/file.c
@@ -427,6 +427,24 @@ static int affs_write_begin(struct file
 	return ret;
 }
 
+static int affs_write_end(struct file *file, struct address_space *mapping,
+			  loff_t pos, unsigned int len, unsigned int copied,
+			  struct page *page, void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	int ret;
+
+	ret = generic_write_end(file, mapping, pos, len, copied, page, fsdata);
+
+	/* Clear Archived bit on file writes, as AmigaOS would do */
+	if (AFFS_I(inode)->i_protect & FIBF_ARCHIVED) {
+		AFFS_I(inode)->i_protect &= ~FIBF_ARCHIVED;
+		mark_inode_dirty(inode);
+	}
+
+	return ret;
+}
+
 static sector_t _affs_bmap(struct address_space *mapping, sector_t block)
 {
 	return generic_block_bmap(mapping,block,affs_get_block);
@@ -436,7 +454,7 @@ const struct address_space_operations af
 	.readpage = affs_readpage,
 	.writepage = affs_writepage,
 	.write_begin = affs_write_begin,
-	.write_end = generic_write_end,
+	.write_end = affs_write_end,
 	.direct_IO = affs_direct_IO,
 	.bmap = _affs_bmap
 };
@@ -793,6 +811,12 @@ done:
 	if (tmp > inode->i_size)
 		inode->i_size = AFFS_I(inode)->mmu_private = tmp;
 
+	/* Clear Archived bit on file writes, as AmigaOS would do */
+	if (AFFS_I(inode)->i_protect & FIBF_ARCHIVED) {
+		AFFS_I(inode)->i_protect &= ~FIBF_ARCHIVED;
+		mark_inode_dirty(inode);
+	}
+
 err_first_bh:
 	unlock_page(page);
 	put_page(page);